Basic magnesium salts are primarily useful as additives for fuels and lubricants. In lubricants such as crankcase lubricating oils, the basic magnesium salts function as detergents and reduce wear mainly by neutralizing acidic products formed during combustion or from the oxidation of the oil components.
When utilized as lubricant additives, these basic magnesium salts are added to the lubricating oil in an amount sufficient to provide the required degree of protection. This is generally in the range which supplies 0.1 to 30% by weight of overbased sulfonate in the formulated oil.
Heretofore it was known to prepare overbased magnesium sulfonates using MgO processes. Generally, these processes used water and methanol as promoters and employed ammonia, ammonium salts, low molecular weight carboxylic acids or salts thereof, oil soluble organic acids including the naphthenics and carboxylics, amines, or amine salts of an acid as secondary promoters.
In U.S. Pat. No. 3,875,737, granted to Kemp and U.S. Pat. No. 4,148,740, granted to Cease et al., there is disclosed an overbased magnesium sulfonate process wherein ammonia or an ammonium compound is used as a promoter. This process required the costly removal of ammonium salts from the product and condensate streams.
In U.S. Pat. No. 4,129,589, granted to Eliades et al., there is disclosed another overbased magnesium sulfonate process which uses low molecular weight carboxylic acids or salts thereof, such as acetic acid as a promoter.
In U.S. Pat. No. 3,629,109, granted to Gergel et al., there is disclosed a multistage carbonation process for preparing an overbased magnesium sulfonate. Mixtures of overbased sulfonates and carboxylates may be formed by reacting a mixture of substantial quantities of sulfonic acids and oil soluble carboxylic acids, with water and alcohol promoters. In Example 24 of the Gergel et al. patent, it is proposed to add quantities of a high molecular weight succinic anhydride, such as polyisobutenyl succinic anhydride, to the product magnesium salt to improve oil solubility. These oil solubility additives were recognized as also improving water tolerance.
Oils containing overbased magnesium sulfonates were not sufficiently water tolerant and failed the Cummins water tolerance test. Specifically where the engine or lubricating oil contained a detergent amount of overbased magnesium sulfonate, such 0.1% to 2.5% Mg metal, the oil failed the Cummins test.
The prior art desired an oil containing an overbased magnesium sulfonate which passed the Cummins test, without the need to post-formation "fix" or "dope" the overbased magnesium sulfonate.
Now there is provided by the present invention an unfixed overbased magnesium sulfonate which when added to an engine or lubricating oil in limited amounts passes the Cummins test.